The invention relates to a measuring apparatus used for testing the connections between at least two subassemblies, comprising a test system for generating a test signal available on an output of the test system and for evaluating an analysis signal produced by a subassembly from the test signal and received on an input of the test system.
Such a measuring apparatus is known, for example, from U.S. Pat. No. 5,029,166 which describes a test system for generating a test signal (Test Data Input TDI), a test clock signal (TCK) and a test control signal (Test Mode Signal TMS) and for receiving an analysis signal (Test Data Output TDO). A boundary scan test is made with this measuring apparatus. Boundary scan cells are positioned, for example, before the inputs of circuit arrangements to be tested, which cells receive either direct or derived test signals. In the boundary scan cells test signals can be combined with input signals. The boundary scan cells are serially connected and the last boundary scan cell produces an intermediate signal or an analysis signal. An analysis signal is applied direct to the test system. The intermediate signal is applied to the next boundary scan cell. This measuring apparatus can be used for testing individual circuit arrangements or connections between the circuit arrangements or subassemblies.
The connections of subassemblies can be tested if the individual subassemblies form a ring-like connection for the test or the measurement. A test input of a subassembly is then connected either to an output of a test system or a subassembly test output of another subassembly. If the interconnections of subassemblies in a system are to be tested, all the subassemblies of the system are to be available and operable. When the system is set up or in a modular system (for example, in telecommunications technology), such a ting configuration cannot be used without further measures being taken.
A further possibility is the use of a star configuration to test subassemblies of a system. However, in that configuration each subassembly needs to have its own control line for a test control signal assigned to each subassembly.